The present invention relates to an anchoring system for use in neurostimulation techniques. More specifically, the present invention relates to a system for anchoring a brain stimulation lead within a cranial burr hole.
The surgical implantation in the human brain of electrode leads to deliver electrical impulses and catheters to deliver drugs in order to provide various types of therapy is known. Electrical stimulation of the brain, for example, can be considered for use to treat chronic pain or movement disorders. Typically, such stimulation is accomplished by the insertion of a multi-electrode lead into the brain, with the electrodes positioned at the location within the brain indicated by the particular condition requiring treatment. Usually, the electrodes are located on the distal end of the lead and a connector is located on the proximal end of the lead, where the lead is connected to a pulse generator, which may be internally or externally powered.
In order to insert the lead into the patient""s brain, a surgeon first drills a hole in the patient""s cranium using a surgical burr. Typically, the hole is 12 to 14 mm in diameter. The surgeon installs a burr hole ring in the burr hole, inserts the lead into the ring and advances the lead through the burr hole ring into the brain. As the surgeon advances the electrode, a test stimulation pulse is delivered to the brain through the electrode and the patient""s response is monitored. When the surgeon observes an appropriate response, the lead is appropriately placed. Placement of the electrode within the brain can be critical, as small changes in position can have an effect on the efficacy of the therapy. Therefore, some type of method for anchoring the lead in place, once the surgeon has determined the optimal location for the electrodes, is required.
Prior methods for anchoring the lead include the application of bio-compatible epoxy or the use of a mechanical anchoring device that is part of or connected to a burr hole ring. For example, U.S. Pat. No. 4,328,813 to Ray (xe2x80x9cRayxe2x80x9d) and U.S. Pat. No. 5,464,446 to Dressen et al. (xe2x80x9cDressenxe2x80x9d) and PCT patent application number WO 98/08554 by Knuth et al. (xe2x80x9cKnuthxe2x80x9d), all of which are incorporated into this document by this reference, describe anchoring systems that involve mechanical anchoring of the lead to a burr hole ring. An article by Jean Siegfried, M. D., Pierre Comte, Ph.D., and Remy Meier appearing in the August, 1983 issue of the Journal of Neurosurgery entitled xe2x80x9cIntracerebral electrode implantation systemxe2x80x9d (xe2x80x9cSiegfriedxe2x80x9d) also describes an anchoring system that involves mechanical anchoring of the lead to a burr hole ring.
Ray describes an anchoring system including an externally threaded burr hole ring that defines a socket into which an anchoring plug is inserted once the lead is correctly positioned within the brain. The anchoring plug is described as being made of sufficiently resilient material that it can be inserted into the socket and deform to accommodate the thickness of the lead. The friction between the socket, the lead and the plug is said to prevent the lead from moving after the plug is inserted into the socket. The anchoring system described in Ray, however, has disadvantages. Because the lead is secured off center, it is difficult to support during installation by stereotactic surgical instruments, which can be used to guide the lead during implantation. Additionally, the lead is subject to movement after the surgeon determines that the lead is correctly positioned but before the surgeon installs the plug, because the lead is unsupported until the plug is actually installed. Finally, the action of installing the plug into the socket can cause movement of the lead.
Dressen describes an anchoring system including a socket with an axial aperture, a plug with a concentric axial aperture and an external circumferential groove, and a cap with means for anchoring the lead in a bent position. The Dressen system has at least the disadvantage of not allowing the lead to be securely anchored by bending it to lay it flat on the surface of the patient""s skull. Dressen""s system also requires anchoring by tightening a suture within the external circumferential groove in the plug. This suture may be inconsistently tightened and may loosen over time.
Knuth and Siegfried describe essentially similar anchoring systems, both of which include, among other elements: (1) a baseplate with a centrally located hole that is adapted to be connected to a burr hole; (2) a compression seal, also with a centrally located hole (e.g., a silicone rubber ring), that is located with its hole aligned with the hole through the baseplate; and (3) a compression screw with a centrally located hole that is used to compress the seal longitudinally so that the seal expands radially inward to engage and therefore anchor the lead. At least one disadvantage associated with the systems described in Knuth and Siegfried is that the twisting of the compression screw may twist the compression seal and thus dislocate the end of the lead before the lead is sufficiently anchored.
Thus, a need continues to exist for an anchoring system for a brain stimulation lead in which the lead is always secure and anchored without applying torsion or axial forces to the lead or otherwise moving the distal end of the lead after it is appropriately positioned.
The design and implementation of a brain lead anchoring system is generally described. The anchor assembly includes an anchoring mechanism within an anchor housing, which has threads on its outer surface so that the housing can be screwed into a burr hole made in the patient""s cranium. The anchoring mechanism preferably includes three locking tabs, each of which moves radially in a channel in the anchor housing relative to the generally centrally located lead path. The locking tabs are spring-loaded in a closed or anchoring position.
The introducer instrument is a generally conical body with a conical aperture that extends axially through the instrument through which the lead is introduced into the anchor assembly and thus the patient""s brain. The introducer instrument also has a distal end having retraction protrusions that fit into complementary slots through the anchor housing. The opening in the distal end of the introducer is large enough that the lead moves easily through the opening. As the introducer instrument is mated to the anchor assembly, the retraction protrusions slide through the slots in the anchor housing and into apertures in the locking tabs, which pushes the locking tabs radially away from the lead path into an open or installation position. When the introducer and anchor assembly are so mated, the conical aperture in the introducer instrument and the centrally located aperture in the anchor assembly define the path on which the lead is introduced into the patient""s brain. The surgeon advances the lead along this lead path using a standard stereotactic frame or a skull mounted guiding device. The lead is advanced into the patient""s brain until the distal end of the lead is correctly positioned. While the lead is still secured in this position within the guiding device, the surgeon activates a mechanism on the introducer instrument or axially withdraws the introducer instrument, causing the retraction protrusions to be withdrawn from the apertures in the locking tabs, which in turn causes the spring-loaded locking tabs to return to the anchoring position, thus xe2x80x9cpinchingxe2x80x9d the lead and anchoring it into position. Thus, the lead is anchored while being supported and without applying torsion or axial forces to the lead.
After the lead is anchored by the locking tabs within the anchor assembly, the surgeon removes the introducer instrument, which exposes the top of the anchor assembly. The surgeon then bends the lead so that it lies in one of the radially extending channels in the top surface of the anchor housing. To complete the installation of the lead, the surgeon inserts the locking cap, which preferably has three locking protrusions extending from its distal surface, into the same slots through which the retraction protrusions of the introducer instrument were inserted. Unlike the retraction protrusions, the locking protrusions hold the locking tabs in the locking position to ensure that the lead remains anchored even if the biasing member that spring-loads the locking tabs closed loses its resilience. The installed locking cap also covers the aperture in the top of the anchor housing.
Additional objectives and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one embodiment of the invention and together with the description, serve to explain the principles of the invention.